LED versus Fluorescent: Lumens per Watt is Only Part of the Story|
Article- November 10, 2013 By Larson Electronics.com
Larson Electronics Explosion Proof Fluorescent Lights
When considering lighting upgrades most professionals consider the initial outlay costs and compare them against the expected savings over a year in order to form a realistic picture of cost effectiveness. When doing a direct comparison between an old system versus a new and considering the savings produced in the form of reduced energy consumption, it is indeed possible to form a basic savings expectation, however this is not a comprehensive view and leaves out a variety of important factors that can affect real world results. Particularly in the case of comparing fluorescent lighting to newer LED technology, there are many less than obvious factors that must be taken into account if an accurate savings expectation can be formulated.
Due to new energy efficiency standards fluorescent lighting technology has undergone several changes that have resulted in an overall significant improvement of its energy efficiency. Older style T12 lamps and magnetic ballasts have been phased out and are being replaced with newer T8 lamps and electronic ballasts which provide much improved performance. Today it is commonplace to find T8 fixtures producing on the order of 80 to 100 lumens per watt of output, putting fluorescent lighting at the top of the efficient lighting ratings in terms of lumen per watt efficiency. However, this does not tell the whole story, and other factors come into play which affect the real world efficiency of fluorescent lighting and brings it a little more down to earth. This is not to say that fluorescent lighting is not an efficient and effective lighting technology, not by any means; only that when comparing fluorescent lighting to other lighting technologies, it is necessary to consider other contributing factors besides just lumen to watt ratios.
LED lighting technology has generated a great deal of excitement in the lighting industry as of late due to its high efficiency and great longevity. Although currently more costly to produce, LED lighting is quickly coming down in price while its lumen per watt ratios continue to climb, putting it into direct competition with linear fluorescent lighting for king of the hill of efficient lighting. LED lighting has yet to become a “mature” technology, but its rapid development is bringing about this maturation quickly, and as of this writing LEDs are now available which do indeed provide some stiff competition for energy efficient fluorescents. LED lighting currently has a real world lumen to watt ratio of around 60 to 100 lumens per watt, with 100 lumens per watt being less common than with fluorescent fixtures, and an average around 80 lumens per watt being closer to the norm. Despite this slightly lower lumen to watt ratio and higher production cost, because of other mitigating factors we will discuss in a moment, LEDs do in fact provide the potential to outperform fluorescents in some applications.
As we mentioned earlier, lumen per watt is the usual defining comparison when most people consider which lighting is the most efficient. But lumen to watt ratios only tell part of the story. One major variation between LED and fluorescent lamps affecting actual lighting performance is their radiating angle. A fluorescent tube radiates its light output 306 degrees over the entire surface of the tube. LED tubes however radiate at an angle of 110 to 120 degrees. Because of this, the actual amount of light reaching the targeted area is greatly affected by radiating angle. For instance, if we were to draw a line straight along the middle of a fluorescent tube, and assume the lower half radiates light downwards, and the upper half radiates upwards, we could roughly say that only half the lamps output is being radiated downwards towards the target area, and the upper half is lost and wasted illuminating unneeded space.
An LED tube on the other hand radiates all of its light downwards. So, if we have an LED tube and a fluorescent tube, and both produce a total of 1500 lumens and have a lumen to watt ratio of 80, then we can say that the fluorescent is only putting 750 lumens on target, while the LED is putting the full 1500 lumens on target. In effect, half the light output of the fluorescent tube is wasted. Granted, this is a big oversimplification, but it demonstrates the point of just why lumen per watt ratios only tell part of the story when it comes to actual efficiency. Even with reflectors and hoods in place, fluorescent lamps lose a significant portion of their light to poor directional control and diffusion, reducing their actual operating efficiency. In applications such as office space or high bay lighting, this can have a significant effect on how practical and cost effective upgrading to a newer lighting system, LED or fluorescent, will actually be. For instance, we could install lower power LED fixtures instead of fluorescent lamps, and still deliver the same amount of light to the targeted area, yet realize even greater reductions in energy use.
Another consideration often overlooked when comparing cost effectiveness between these two lighting technologies is overall operating costs rather than just costs associated with energy use. Lamp life is considered part of overall operating costs, and with LEDs usually lasting twice as long as fluorescent tubes LEDs have the upper hand. However, fluorescent lamps also utilize a ballast, and with ballasts having a service life on average of 50,000 hours, they will have to be replaced every second relamping, significantly increasing operating costs. LEDs on the other hand are entirely solid state and will not require this added expense.
As can be seen, there is much more to determining actual efficiency and cost effectiveness when comparing competing lighting technologies. Factors such as intended application, design differences, and expected ROI will play a large role in determining just which upgrade solution best fits your needs. The best results are obtained when one gains a broader understanding of all the factors that set one lighting technology apart from another, and then applies that knowledge towards forming a real world expectation of performance.